JPH10138332A - Biaxially stretched polyamide film and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially stretched polyamide film having laminar silicate uniformly dispersed therein and excellent in capacities such as transparency, rigidity or gas barrier properties and a method for stably producing the same. SOLUTION: After the moisture content of a non-stretched sheet using a polyamide resin compsn. consisting of 90-99.99wt.% of polyamide and 10-0.01wt.% of laminar silicate as a main raw material is adjusted to 1.3-10wt.%, this sheet is biaxially stretched in its longitudinal and lateral directions within a temp. range of 90 deg.C-(m.p. of polyamide -5) deg.C so that area magnification brecomes 4.0 times or more to produce a biaxially stretched polyamide film. This laminar silicate obtained by this manufacturing method is uniformly dispersed in polyamide so that the thickness thereof is 6-12Å and the interlaminar distance thereof is 20Å or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched polyamide film in which a layered silicate is uniformly dispersed and which is excellent in transparency, rigidity, gas barrier properties and the like.

[0002]

2. Description of the Related Art Polyamide films have excellent mechanical properties, toughness, heat resistance, pinhole resistance, oil resistance, gas barrier properties, and transparency, and are used for packaging of foods, pharmaceuticals, sundries, etc. ing. Among the above performances, the gas barrier property is an important property for preventing oxidation of the contents. Polyamide films are excellent in gas barrier properties, particularly oxygen barrier properties, and are more useful as packaging materials than general-purpose films such as polyolefins. However, since the polyamide film has significantly reduced gas barrier properties due to moisture absorption, a method for solving this problem has been desired. As a method of enhancing gas barrier properties while maintaining excellent properties as a packaging material for a polyamide film, a method of coating a polyvinylidene chloride resin (PVDC), a method of evaporating an inorganic substance such as aluminum or silicon dioxide, or A method of forming a multilayer with another resin composition having excellent gas barrier properties, such as an ethylene-vinyl alcohol copolymer or a polyamide (MXD6 nylon) from meta-xylylenediamine and adipic acid, is known. However, the method of coating PVDC requires a separate coating line, complicates the production process, and makes it difficult to recycle the polyamide resin. Further, the method of depositing an inorganic substance has problems that the speed of the deposition step is low, the toughness of the obtained film is reduced, and recycling is difficult. Furthermore, in the method using multiple layers, there are problems in the complexity of the extrusion molding process and the recyclability due to the increase in the configuration of the extrusion layer.

In recent years, as a method for improving the rigidity and gas barrier properties of a polyamide film, a method using a polyamide in which layered silicate is uniformly dispersed as a raw material has been proposed. For example, a film comprising a polyamide and a layered silicate such as montmorillonite has been proposed (JP-A-2-105856).

Japanese Patent Application Laid-Open No. 3-262633 discloses that the method proposed in Japanese Patent Application Laid-Open No. 2-105856 reduces the transparency of a film at the time of stretching, which is inconvenient for use as a packaging material. For this reason, the unstretched polyamide film in which the layered silicate is uniformly dispersed
A method of stretching at 1.2% by weight or less has been proposed. Further, as a method of improving the decrease in transparency at the time of stretching, a method of adding a hindered phenol compound to a polyamide resin composition in which a layered silicate is uniformly dispersed (Japanese Unexamined Patent Application Publication No.
JP-A-80259), a method of adding a silane coupling agent and / or a titanate coupling agent (Japanese Patent Laid-Open No. 4-11 / 1990).
0347), a method of adding a hindered phenol compound, and a silane coupling agent and / or a titanate coupling agent (Japanese Patent Application Laid-Open No. 4-178459).
Although each of them has been proposed, the effect of improving transparency reduction was not sufficient.

In each of the above publications, the stretching ratio of the film is only twice in each of the longitudinal and transverse directions in each of the examples. However, the excellent characteristics of the polyamide film as a packaging material are not described. In order to exhibit the effect, it is generally necessary to stretch at a draw ratio of 2.5 to 4.0 times which is larger than this. In general, the decrease in transparency at the time of stretching becomes remarkable with an increase in the stretching ratio, and when high stretching conditions such as those used industrially are used,
It has been difficult to obtain a stretched polyamide film having sufficiently high transparency by using any of the methods proposed in the above publications.

Further, when a stretched film is produced using a polyamide resin composition in which a layered silicate is uniformly dispersed as a raw material, troubles in cutting the film are liable to occur, and in particular, the layered silicate is used to improve gas barrier properties. When the addition amount of the silicate is increased, cutting frequently occurs, and improvement has been desired.

The present inventors have previously used a resin composition obtained by blending a swellable fluoromica-based mineral with a polyamide as a raw material and have excellent properties such as rigidity, gas barrier properties, retort resistance and dimensional stability. A biaxially stretched polyamide film and a method for producing the same have been proposed (JP-A-8-120099).
The transparency of the obtained film was not sufficient, and further improvement was desired.

[0008]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and has a biaxial structure in which a layered silicate is uniformly dispersed and which is excellent in transparency, rigidity, gas barrier properties and the like. An object of the present invention is to provide a stretched polyamide film and a method for stably producing the same.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a polyamide resin composition containing a layered silicate is stretched under a specific condition to obtain transparency. The present inventors have found that a biaxially stretched polyamide film having excellent rigidity, gas barrier properties, and the like can be stably produced, and arrived at the present invention.

That is, the gist of the present invention is as follows. (1) 90 to 99.99% by weight of polyamide and 10 to 10% of layered silicate
After adjusting the moisture content of an unstretched sheet using a polyamide resin composition consisting of 0.01% by weight as a main raw material to 1.3 to 10% by weight, 90 ° C or more (melting point of polyamide-5)
A method for producing a biaxially stretched polyamide film, wherein the film is biaxially stretched in a machine direction and a transverse direction at a temperature of not more than ° C so as to have an area magnification of 4.0 times or more. (2) A biaxially stretched polyamide film obtained by the production method according to the above (1), wherein the layered silicate is uniformly dispersed in a polyamide with a thickness of 6 to 12 mm and an interlayer distance of the layered silicate of 20 mm or more. .

[0011]

DETAILED DESCRIPTION OF THE INVENTION Preferred polyamides in the present invention include nylon 6, nylon 46 and nylon.
66, nylon 69, nylon 610, nylon 612, nylon 116, nylon 11, nylon 12, nylon 6I, nylon 6/66, nylon 6T / 6I, nylon 66 / 6T,
Polybis (4-aminocyclohexyl) methandodecamide (nylon PACM12), polybis (3-methyl-4)
-Aminocyclohexyl) methandodecamide (nylon dimethyl PACM12), polymethaxylylene adipamide (nylon MXD6), polyundecamethylene terephthalamide (nylon 11T), polyundecamethylene hexahydroterephthalamide (nylon 11T (H)) And the like, and two or more thereof may be used in combination, or a copolymer thereof may be used. In addition, I is an isophthalic acid component, T
Represents a terephthalic acid component. Of these, particularly preferred are nylon 6, nylon 46, nylon 66, nylon 11, nylon 12, nylon 610, copolymerized polyamides thereof, and mixed polyamides, and most preferred is nylon 6.

Although the relative viscosity of the polyamide is not particularly limited, 98% sulfuric acid is used as a solvent at a temperature of 25 ° C. and a concentration of 1 g / dl.
It is preferable that the relative viscosity determined under the conditions described above is in the range of 1.5 to 5.0. When the relative viscosity is less than 1.5, the mechanical performance of the film is reduced, and when the relative viscosity is more than 5.0, the film-forming properties are undesirably reduced.

The layered silicate used in the present invention is:
The thickness of the layer is 6 to 12 mm, and the average length of one side of the layer is 0.001 to 10
Those having a crystal unit of μm are preferred.

The layered silicate used in the present invention includes montmorillonite, saponite, paiderite,
Examples include smectite clay minerals such as nontrolite, hectorite, and stevensite, vermiculite clay minerals, halloysite clay minerals, and the like. These layered silicates may be natural or synthetic. Among these, montmorillonite is particularly preferred in terms of performance such as transparency, rigidity and gas barrier properties of the obtained biaxially stretched polyamide film.

The compounding amount of the layered silicate is 90 to 9% of polyamide.
9.99% by weight and 10 to 0.01% by weight of layered silicate. If the amount of the layered silicate is less than 0.01% by weight, the effect of the present invention is small. If the amount exceeds 10% by weight, the resin composition is thickened and extrusion processing becomes difficult, or the toughness of the obtained film is reduced. It is not preferable because it lowers.

The layered silicate in the biaxially stretched polyamide film obtained by using the polyamide resin composition of the present invention accounts for 50% by weight of a multilayer having an average of 5 or less layers.
As described above, usually 70% by weight or more of the layered silicate is uniformly dispersed in the polyamide matrix while maintaining a distance of 20 ° or more without forming local agglomerates. In order to promote uniform dispersion of the layered silicate, for example, as proposed in JP-A-62-74957, the layered silicate is brought into contact with a swelling agent, and the interlayer is preliminarily expanded and the monomer is interposed between the layers. It is also possible to use a method in which the molecules are easily incorporated, mixed with a polyamide monomer, and then polymerized.

The polyamide resin composition of the present invention contains a pigment, a heat stabilizer, an antioxidant, a weathering agent, a flame retardant, a plasticizer, a release agent and other reinforcing materials as long as the properties are not significantly impaired. It is also possible to add. Examples of such heat stabilizers and antioxidants include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, and halides of alkali metals. These additives such as a heat stabilizer, an antioxidant, and a weathering agent are generally added during melt-kneading or polymerization.

As a method for producing the film of the present invention, known methods such as a T-die method and an inflation method can be used.

For example, in the T-die method, a polyamide resin composition in which layered silicate is uniformly dispersed is melted in an extruder, extruded from a T-die into a sheet, and cast on a cooling drum to form an unstretched sheet. obtain. At the time of cooling and solidification, the melted sheet is cooled by air nozzle method, air knife method,
For example, a method of electrostatically adhering to a cooling roll can be used.

The unstretched sheet thus obtained is immersed in a hot water bath, and the moisture content is 1.3 to 10% by weight, preferably 2 to 10% by weight.
After adjusting to 7% by weight, at a temperature of 90 ° C. or more and (polyamide melting point−5) ° C. or less, preferably 120 or more and (polyamide melting point−10) ° C. or less, the longitudinal direction (MD) and the horizontal direction Each film is stretched in the direction (TD) at a draw ratio of 2 times or more, and then heat-treated at a temperature of 100 ° C. or higher and the melting point of the polyamide or lower. If the moisture content of the unstretched sheet is less than 1.3% by weight or more than 10% by weight, uneven stretching (neck stretching) or cutting in the stretching step is likely to occur, which is not preferable.

When the stretching ratio is smaller than 2 times, the strength of the obtained film is low, and when the stretching temperature is lower than 90 ° C.,
When the film is stretched, the transparency of the film is impaired, or a cutting trouble occurs. If the stretching temperature exceeds (melting point of polyamide -5) ° C., the film partially melts, causing whitening or fusing trouble of the film. Therefore, it is not preferable.

As a method for adjusting the moisture content, for example, a method is preferable in which a water tank having a plurality of rolls is installed on a production line, and an unstretched sheet is passed through the water tank along the rolls to continuously absorb water. .

As the stretching method, any of a tenter simultaneous biaxial stretching method and a sequential biaxial stretching method using a roll and a tenter can be used.

On the surface of the obtained film, corona discharge treatment, surface hardening treatment, plating treatment,
A physicochemical surface treatment such as a cleaning treatment, a coloring treatment, a paint finishing treatment or a coating may be added.

The polyamide film of the present invention can be laminated with another polymer film according to the purpose. As other polymer films, low-density polyethylene film, high-density polyethylene film, polypropylene film, ethylene-vinyl alcohol copolymer film,
Ionomer resin films, polyester films, other polyamide films, etc.

[0026]

Although it is not clear why the transparency of the film is reduced when an unstretched sheet using a polyamide resin composition containing a layered silicate as a raw material is stretched,
It is presumed that when the film is stretched, a large stress is concentrated on the interface between the local agglomeration of the layered silicate and the polyamide matrix, causing interface delamination, and the formation of voids around the agglomeration. In the present invention, using a raw material in which the layered silicate is uniformly dispersed, the moisture content of the unstretched sheet is reduced.
By stretching after adjusting to 1.3 to 10% by weight, stress concentration at the interface is unlikely to occur even if there is agglomeration of layered silicate, preventing the formation of voids due to interface delamination and excellent transparency It is believed that a stretched stretched polyamide film is obtained.

[0027]

Next, the present invention will be described more specifically with reference to examples. In addition, the raw materials and measuring methods used in the evaluation of the examples and comparative examples are as follows.

1. Raw material For 100 g of montmorillonite having an average particle size of 1 μm,
10 liters of a 1N aqueous solution of 12-aminododecanoic acid chloride was mixed and stirred. Next, this was filtered, washed with water, and dried to obtain a complex of montmorillonite and ammonium 12-aminododecanoate. In a closed reaction vessel equipped with a stirrer, 10 kg of ε-caprolactam, 1 kg of water, and a predetermined amount of the complex were mixed so that the montmorillonite content in the resin composition became the amount shown in Table 1, The mixture was stirred at 80 ° C. until the reaction system became homogeneous. Next, the reaction system
The mixture was heated to 260 ° C. and stirred for about 1 hour in a state where the pressure in the reaction vessel was 15 kg / cm ² . Return the pressure to normal pressure, 260 ℃
For about 1 hour, and further stirred for about 1 hour under a nitrogen stream while removing water in the reaction system. After the completion of the reaction, the molten reaction product was discharged into a water bath in a strand form, and cut with a pelletizer to obtain a pellet of a polyamide resin composition in which montmorillonite was uniformly dispersed.
This pellet was treated in hot water at 95 ° C. for about 6 hours to extract soluble components, and then dried at 80 ° C. under reduced pressure. By the above method, nylon 6 resin compositions having different montmorillonite contents and relative viscosities were obtained. The montmorillonite content in the resin composition was measured by ash measurement, and the relative viscosity was measured in 98% sulfuric acid at a temperature of 25 ° C. and a concentration of 1 g / dl. When the X-ray diffraction of the obtained resin composition pellets was measured, no peak indicating that the interlayer distance of montmorillonite was 20 ° or less was not detected in any of the pellets.

2. Measurement Method (1) Tensile Modulus The longitudinal direction of the film was measured using an Autograph DSS-500 manufactured by Shimadzu Corporation in accordance with ASTM D-882. (2) Oxygen permeability Using MOCON OX-TRAN 100A manufactured by Modern Control Co., it was measured at 20 ° C. and 0% RH according to ASTM D-1434. (3) Haze Using a haze meter manufactured by Tokyo Denshoku Co., Ltd., ASTM D-1003
It measured according to. (4) Stability in the Stretching Step In a continuous film formation for 3 hours, the time t until the work interruption due to the cutting trouble in the stretching step occurred 5 times was recorded, and the stability in the stretching step was evaluated.

Examples 1 to 10 The nylon 6 resin composition containing montmorillonite shown in Tables 1 and 2 was melt-extruded at a cylinder temperature of 260 to 270 ° C. using a single screw extruder equipped with a T die having an inner diameter of 65 mm. After that, it was cast on a cooling roll to obtain an unstretched sheet having a width of 250 mm. The thickness of the unstretched sheet was adjusted by the rotation speed of the cooling roll so that the thickness of the finally obtained stretched film was 15 μm. The obtained unstretched sheet was guided into a constant temperature water tank in which a plurality of rolls were arranged.
Water was absorbed so that the water content shown in FIG. The moisture percentage is
The temperature was adjusted according to the temperature of the water bath and the immersion time of the unstretched sheet in the water bath. Next, the water-absorbed unstretched sheet was guided to a tenter-type simultaneous biaxial stretching machine and stretched simultaneously in the machine and transverse directions at the stretching temperature and the stretching ratio shown in Tables 1 and 2;
For 2 seconds. The physical properties of the obtained biaxially stretched polyamide film are shown in Tables 1 and 2.

[0031]

[Table 1]

[0032]

[Table 2]

Comparative Examples 1 to 6 The same as Example 1 except that the nylon 6 resin composition containing montmorillonite shown in Tables 3 and 4 was used and the moisture content and stretching conditions shown in Tables 3 and 4 were used. A biaxially stretched polyamide film was produced by the method described above. The physical properties of the obtained biaxially stretched polyamide film are shown in Tables 3 and 4. In addition,
In Comparative Example 6, necking was not performed during stretching, and a uniform stretched film could not be obtained.

Comparative Example 7 A biaxially stretched polyamide film was prepared in the same manner as in Example 1 except that nylon 6 (relative viscosity: 3.1) containing 800 ppm of silica having an average particle size of 1.8 μm was used as the nylon 6 resin composition. Manufactured. Table 4 shows the physical properties of the obtained biaxially stretched polyamide film.

Comparative Example 8 The moisture content of the unstretched sheet was set to 0.8% by weight, and the stretching temperature was set to 80%.
A biaxially stretched polyamide film was produced in the same manner as in Comparative Example 7 except that the temperature was changed to ° C. Table 4 shows the physical properties of the obtained biaxially stretched polyamide film.

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

According to the present invention, there is provided a biaxially stretched polyamide film in which layered silicate is uniformly dispersed and which has excellent properties such as transparency, rigidity and gas barrier properties.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FIB29L 7:00 (72) Inventor Tadashi Shuto 23 Uji Kozakura, Uji-shi, Kyoto 23 Unitika Co., Ltd. Central Research Laboratory (72) Inventor Mioko Watanabe 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Research Institute Central Research Laboratory

Claims (4)

[Claims] An unstretched sheet using a polyamide resin composition comprising 90 to 99.99% by weight of a polyamide and 10 to 0.01% by weight of a layered silicate as a main raw material has a water content of 1.3 to 1.3%.
After adjusting to ~ 10% by weight, the film is biaxially stretched in the vertical and horizontal directions at a temperature of 90 ° C or more and (melting point of polyamide-5) ° C or less so that the area magnification becomes 4.0 times or more. A method for producing a biaxially stretched polyamide film. 2. The method according to claim 1, wherein the layered silicate is montmorillonite. 3. Biaxially obtained by the production method according to claim 1 or 2, wherein the layered silicate is uniformly dispersed in polyamide in a state in which the thickness of the layered silicate is 6 to 12 mm and the interlayer distance of the layered silicate is 20 mm or more. Stretched polyamide film. 4. The biaxially stretched polyamide film according to claim 3, wherein the haze of the film is 4.2 or less.